This invention relates generally to manhole or manway covers, and more particularly to a device to assist in the lifting of such cover.
Because of the weight of manway lids, various efforts have been made to make it easier to open them. Usually such devices are associated with the lid hinge assembly. U.S. Pat. Nos. 4,137,669 and 5,038,520 use conical compression springs pulling a rod to assist. U.S. Pat. No. 5,184,422 also uses a compression spring, but vertically oriented to assist the limited distance left of a lid which swings away from the manway in a horizontal plane. U.S. Pat. No. 5,394,650 uses torsion springs around a horizontal hinge pin to assist the lid lifting. Spring balanced lids have been available in the marine industry for at least twenty years. A variety of Cen-Tex brand hatches with spring-assisted lids is available from Timco Industries, Inc. of New Albany, Ind. These use torsion springs to balance round, rectangular, and elongate oval shapes of lids. Some aspects of inconvenience in the mounting or use of one or more of these devices are the necessity of attaching one or more components of the balancing assembly to the manway frame or cover, the inability to hold the cover open adequately, the inability or difficulty in adjusting the balancing force to prevent the cover from dropping, and the necessity to use welding equipment for some installations to manway frames. The difficulty of adapting the balancing assembly to various styles of covers and arrangements of hinging the cover to the manway frame has been an ongoing problem.
Described briefly, according to a typical embodiment of the present invention, a balancer mount is connected to the manway hinge and engages the manway frame to locate the lifter assembly. A cam is situated in the mount for pivotal action on the hinge and has a portion to engage the lid, and a portion to receive a force applied by a balancing spring seated in the mount. A spring adjustment device is provided at a readily accessible location on the mount.
In one embodiment, the lid lifter assembly is arranged to provide the lid lifting assist at a location between the hinge arms of the lid. In another embodiment, the lifter assembly is mounted outboard of the hinge arms and applies the lift assist at a location outboard of the hinge arms but adjacent one of the hinge arms. In both instances, the lifter assembly has a housing with at least one arm portion engaging the lid hinge mounting bracket of the manway to hold and control the lifter assembly housing relative to the manway.